DESCRIPTION (provided by applicant: The broad objectives of this study are to identify the optimal adult-derived tissue source (bone marrow, muscle, or adipose tissue) for isolation of mesenchymal progenitor cells capable of differentiating into cartilage or bone. Successful completion of the studies outlined in this proposal will provide a strong foundation for our long term goal of refining present strategies for improved clinical outcome of stem cell enhanced restoration of bone or cartilage. The hypothesis of this proposal is that a progenitor cell subpopulation with a capacity to preferentially differentiate into cartilage or bone can be identified and isolated from other cell subpopulations derived from bone marrow aspirate, muscle, or adipose tissue. As a first step towards reaching our long-term objective we will define unique features of subpopulations of mesenchymal progenitor cells (MPC)s derived from adult-derived bone marrow aspirate, muscle, and adipose tissues. We will then quantify the number of stem cells that can be obtained from each tissue, and finally, we will determine which tissue(s) provides the optimal MPC source for differentiation into cartilage or bone. To achieve these goals, will use single cell cloning, gene expression levels with quantitative RT PCR, flow cytometric analyses of several cell surface protein markers, and immunohistochemical techniques. Expanding our knowledge of MPC subpopulations is an important step toward understanding stem cell physiology and is essential for critical assessment of MPC-based grafting procedures. The expectation is that completion of the studies outlined in this proposal will provide important insight into the identification and isolation of MPC subpopulations. A more precise understanding of the heterogenous population of MPC obtained from adult tissues should improve differentiation of MPCs into cartilage and bone. We anticipate that these findings will have a major impact on the clinical use of MPCs in targeted tissue repair applications. The research in this proposal is important for improving the health of millions afflicted with arthritis or bone diseases. Our studies will expand the present knowledge base concerning adult tissue-derived stem cell biology with a specific focus on the clinical application of stem cells for repair of joints and bones.